The present invention relates to a process for the production of ethylenically unsaturated carboxylic acids or esters, particularly α, ß unsaturated carboxylic acids or esters, more particularly acrylic acids or esters such as (alk)acrylic acids or alkyl (alk)acrylates particularly (meth)acrylic acid or alkyl (meth)acrylates such as methyl (meth)acrylates by the condensation of carboxylic acid esters with formaldehyde or a source thereof in the presence of bases, in particular, but not exclusively, a process for the production of (meth)acrylic acid or alkyl esters thereof, for example, methyl methacrylate, by the condensation of propionic alkyl esters, for example methyl propionate, with formaldehyde or a source thereof in the presence of such a base. The invention is particularly relevant to the production of methacrylic acid (MAA) and methyl methacrylate (MMA).
Such acids or esters may be made by reacting an alkanoic ester of the formula R3—CH2—COOR4, where R3 and R4 are each, independently, a suitable substituent known in the art of acrylic compounds such as an alkyl group, especially a lower alkyl group containing, for example, 1-4 carbon atoms, with a suitable methylene source such as formaldehyde. Thus, for instance, methacrylic acid or alkyl esters thereof, especially methyl methacrylate, may be made by the catalytic reaction of methyl propionate, with formaldehyde as a methylene source.
U.S. Pat. No. 485,070 describes the production of α,ß unsaturated aliphatic carboxylic acids by the vapour phase condensation of a saturated aliphatic monocarboxylic acid with formaldehyde using a caesium catalyst supported on a porous silica gel. The production of methacrylic acid from propionic acid and formaldehyde in the presence of the caesium/silica catalysts is carried out at temperatures ranging from 273° C. to 408° C. with the selectivity for methacrylic acid ranging from 81 to 88%.
As mentioned above, a known production method for MMA is the catalytic conversion of methyl propionate (MEP) to MMA using formaldehyde. U.S. Pat. No. 6,544,924 describes the production of ethylenically unsaturated acids or esters by the catalytic reaction of an alkanoic acid or ester, especially methyl propionate, with formaldehyde in the presence of a silica supported catalyst. The production of methyl methacrylate (MMA) and methacrylic acid (MA) from methyl propionate, methanol and formalin using these catalysts was carried out at 350° C. and resulted in yields of MMA and MA between 3 and 12% and selectivities for MMA and MA between 88 and 97%.
The problem with heterogenous systems is that high temperatures are required which increases expense and also increase the production of unwanted by-products.
WO00/58298 discloses that drying agents can be used in the reaction of lactones with a source of formaldehyde in the presence of a base to remove water, the sources of formaldehyde are polyoxymethylene or aldehydes. The lactone intermediates are very stable to hydrolysis and are highly activated due to the ring structure and both heterogenous and homogenous base catalysts are discussed. On the other hand, a linear ester is much more susceptible to hydrolysis and is much less activated.